1. Field of the Invention
The invention relates to a remote control device for automotive working devices; which can be used in particular in ground-compaction devices.
2. Description of the Related Art
One way of remotely controlling e.g. automotive working devices is to provide a cable connection between the working device and a transmitter of a remote control device, several wires being accommodated in said cable connection. On the one hand, the cable connection serves to transmit control commands from the transmitter of the remote control device to the working device. Furthermore, the transmitter is supplied with power from the working device by means of the cable connection. As a consequence, it is possible to maintain a continuous operation with the working device.
In the case of a working device which utilises this type of remote control, owing to the predetermined length of the cable the aforementioned cable connection means that the operator of the working device can only remain within a designated operating area. In other words, the length of the cable is dimensioned such that the operator is not able to walk in front of the moving working device. Furthermore, the operating area provided for the operator is rendered safe by means of safety devices, e.g. protective bars and pressure bars or the like which serve to stop the working device or to reverse the direction of travel of the working device, if the operator comes into contact with the safety device.
However, when operating this type of working device on a building site, it is not entirely impossible to cause damage to the safety devices provided on said device which means that it is no longer possible to guarantee the safety of the operator. For example, a protective bracket can become bent or can tear off from the working device, as a result of which it is no longer possible to stop the operation of the moving working device in a dangerous situation. A further disadvantage of remote control by means of the cable connection resides in the fact that the restricted length of the cable forces the operator to follow the working device constantly and to remain in close proximity thereto. As a result, the operator is continuously exposed to the noise, possible exhaust gases and/or vibrations of the working device.
To obviate the aforementioned disadvantages, a remote control device having an infrared system is known, wherein a modulated infrared light is transmitted from a transmitting unit to a receiving unit, which is disposed on the automotive working device, for the purpose of communicating the control commands. In accordance with current safety directives, the operator of this type of infrared remote control device is constantly in visual contact with the working device, wherein the transmitting unit is to be aligned with the receiving unit provided on the working device. As soon as the operator ceases to direct the infrared beam, which is output by the transmitting unit, to the receiving unit, e.g. as a result of a fall, the reception of the infrared signal and subsequently the operation of the working device are interrupted and the working device is shut off.
DE 42 21 793 C1 discloses an infrared remote control for automotive ground-compaction devices which uses a control device carried by the operator to transmit not only the infrared control radiation provided for the functional control of the working device but also short-range infrared radiation at a substantially lower intensity than the control radiation, so that this short-range radiation can only be received with sufficient intensity in the immediate surrounding area of the transmitter. Upon reception of this short-range radiation, the receiving unit on the working device serves to suppress the generation of electrical signals which are caused by the control radiation and which otherwise cause the working device to move.
In the case of this infrared remote control, the working device can be operated for as long as it is located within receiving range of the control radiation but outside the range of the short-range radiation. If the distance between the operator and the working device is less than a predetermined safety distance, i.e. if the short-range radiation is received by the receiving unit provided on the working device, the working device will be shut off.
One disadvantage of infrared systems is generally that the required beam power causes the transmitting unit to consume a substantial amount of power.
If during usage of the working device a battery provided for supplying power to the transmitting unit, or a transmitting storage cell has run out, this can lead to adverse interruptions in operation. Furthermore, there is a safety risk in the event that the discharge of the battery or the transmitter storage cell makes it no longer possible to control the working device perhaps at an inopportune moment.
DE 41 39 041 A1 describes a remote control device which can be operated both as a wireless system and as a system comprising a wire connection. A detector establishes whether a signal transmission cable is connected to the device, and outputs a corresponding signal to switching means which switch the device between the wireless system and the system comprising the wire connection. During the wire-connection operation, the control signals are transmitted via the cable which connects a transmitter to a receiver. In addition, the cable serves to supply power to the transmitter.